java分页使用本地线程方式

本内容使用的另一种方式实现分页功能，以前我们做分页都是在Controller的方法上传pageNum和pageSize这2个值，要么以形参方式(get请求)，要么以实体方式(post请求)，

现在我们可以使用ThreadLocal是一个线程内部的存储类，可以在指定线程内存储数据，数据存储以后，只有指定线程可以得到存储数据，这样就不需要我们在方法上传值了。

1、创建本地分页线程实体类

package com.zc.bean;

public class PaginationContext {
    // 定义两个threadLocal变量：pageNum和pageSize
    private static ThreadLocal<Integer> pageNum = new ThreadLocal<Integer>(); // 保存第几页
    private static ThreadLocal<Integer> pageSize = new ThreadLocal<Integer>(); // 保存每页记录条数

    /**
     * pageNum ：get、set、remove
     */
    public static int getPageNum() {
        Integer pn = pageNum.get();
        if (pn == null) {
            return 0;
        }
        return pn;
    }

    public static void setPageNum(int pageNumValue) {
        pageNum.set(pageNumValue);
    }

    public static void removePageNum() {
        pageNum.remove();
    }

    /**
     * pageSize ：get、set、remove
     */
    public static int getPageSize() {
        Integer ps = pageSize.get();
        if (ps == null) {
            return 0;
        }
        return ps;
    }

    public static void setPageSize(int pageSizeValue) {
        pageSize.set(pageSizeValue);
    }

    public static void removePageSize() {
        pageSize.remove();
    }
}

2、创建分页拦截器

package com.zc.app.handler;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.zc.bean.PaginationContext;
import com.zc.common.utils.StringUtils;


public class PageFilter implements Filter {

    private static final Logger logger=LoggerFactory.getLogger(PageFilter.class);
    private String[] prefixIgnores;
    
    public PageFilter() {
    }

    @Override
    public void destroy() {
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        
        if (isIgnore(httpRequest.getRequestURI())) {//放行
            chain.doFilter(request, response);
        }else{
            PaginationContext.setPageNum(getPageNum(httpRequest));
            PaginationContext.setPageSize(getPageSize(httpRequest));
            try {
                chain.doFilter(request, response);
            }
            // 使用完Threadlocal，将其删除。使用finally确保一定将其删除
            finally {
                PaginationContext.removePageNum();
                PaginationContext.removePageSize();
            }
        }
        
    }

    /**
     * 获得pager.offset参数的值
     * 
     * @param request
     * @return
     */
    protected int getPageNum(HttpServletRequest request) {
        int pageNum = 1;
        try {
            String pageNums = request.getParameter("pageNum");
            if (pageNums != null && StringUtils.isNumeric(pageNums)) {
                pageNum = Integer.parseInt(pageNums);
            }
        } catch (NumberFormatException e) {
            logger.error(e.getMessage(), e);
        }
        return pageNum;
    }

    /**
     * 设置默认每页大小
     * 
     * @param request
     * @return
     */
    protected int getPageSize(HttpServletRequest request) {
        int pageSize = 10; // 默认每页10条记录
        try {
            String pageSizes = request.getParameter("pageSize");
            if (pageSizes != null && !("".equals(pageSizes)) && StringUtils.isNumeric(pageSizes)) {
                pageSize = Integer.parseInt(pageSizes);
            }
        } catch (NumberFormatException e) {
            logger.error(e.getMessage(), e);
        }
        return pageSize;
    }

    @Override
    public void init(FilterConfig config) throws ServletException {
        String contextPath=config.getServletContext().getContextPath();
        String ignores=config.getInitParameter("prefixIgnores");
        if (null!=ignores && !("".equals(ignores))) {
            String[] ignoresArray=ignores.split(",");
            prefixIgnores=new String[ignoresArray.length];
            for (int i = 0; i < ignoresArray.length; i++) {
                prefixIgnores[i]=contextPath+ignoresArray[i];
            }
        }
    }

    
    /**
     * @description 判断uri是否执行过滤
     * @param uri
     * @return true=不过滤
     */
    private boolean isIgnore(String uri){
        boolean flag=false;
        if (null!=prefixIgnores && null!=uri) {
            for (int i = 0; i < prefixIgnores.length; i++) {
                if (uri.startsWith(prefixIgnores[i])) {
                    flag=true;
                }
            }
        }
        return flag;
    }
}

3、使用

PageHelper.startPage(PaginationContext.getPageNum(), PaginationContext.getPageSize());
PageList<Company> fileList = companyMapper.getPageList(companyDTO);